US Patent 8728607 Ceramic honeycomb structure and its production method

A ceramic honeycomb structure comprising a ceramic honeycomb body having cell walls defined by a large number of longitudinally extending cells, and an outer peripheral wall formed on an outer peripheral surface of the ceramic honeycomb body, the outer peripheral wall being formed by coating longitudinally extending grooves defined by cell walls on the outer peripheral surface of the ceramic honeycomb body with a coating material, and the outer peripheral wall having higher hardness in its outer peripheral portion than in its inside portion in a thickness direction.